Electrosurgical instruments for delivering radio frequency (RF) electrical energy into tissue are known. For example, U.S. Pat. No. 5,868,740 discloses electrosurgical probes that include a plurality of wire electrodes that may be advanced into tissue from the distal end of a cannula. The electrodes may be energized with RF energy in a monopolar or bipolar mode to heat and/or necrose a target tissue region. Such probes have been suggested for treating tumors within organs, such as the liver, kidney, pancreas, stomach, lungs, and spleen.
One concern with RF ablation is the “heat sink” effect, which may occur because of the vascular nature of the tissue being treated. For example, within the liver, RF energy may be delivered to heat and necrose a tumor. If the tumor is located near a large vessel, blood passing through the vessel may conduct heat away from the tumor. This may cause the heat to be distributed unevenly, possibly resulting in tumor cells adjacent to the vessel not being sufficiently heated and/or destroyed. To ensure that the cells nearer to the vessel are sufficiently heated, additional energy may be applied to the tumor, but this may expand the heated region into tissue located away from the vessels, which may risk damaging healthy tissue adjacent to the tumor.
Accordingly, apparatus and methods for facilitating heating or otherwise treating tissue would be useful.